摘要:

High‐temperature superconductor GdBa2Cu3O7thin films were growninsituon LaAlO3single‐crystal substrates by dc magnetron sputtering using a single planar target. 93% samples had a zero resistance transition temperatureTc0more than 90 K and a transition width less than 1 K. The best films had aTc0of 92.5 K, a transition width of 0.57 K, and a critical current density of 3.6×106A/cm2at 77 K. The reproducibility is very good. X‐ray diffraction analysis showedcaxis normal to the film’s surface.

ISSN:0003-6951    

DOI:10.1063/1.103253

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Flux creep data are reported which clearly demonstrate a dramatic enhancement in the pinning potential for magnetic vortices (fluxoids) in a Tl2Ca2Ba2Cu3Oysingle crystal upon irradiation with 4.5 MeV protons. The creep rate is markedly reduced between 5 and 80 K, and the effective pinning potential is quadrupled from ≊100 to ≊400 meV at 20 K in a field of 50 mT. This stronger pinning enhances the magnetization hysteresis and hence the inferred low‐field critical current density by a factor of 5 at 40 K.

ISSN:0003-6951    

DOI:10.1063/1.103254

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Most of the transition metal elements incorporated into the lattice of YBa2Cu3O7−&dgr;are known to severely suppress the superconducting transition temperature. In this work, we show that an essentially complete recovery of the 90 K superconductivity can be achieved by partial melt processing of the material doped with Zr, Ta, Ti, Pt, Rh, and Re, which is attributed to second phase particles draining the dopant elements away from the matrix. Such a full recovery ofTcis not obtained in the case of Nb, V, Ni, Fe, Co, Pd, and Ru. The results are of technological interest in view of the need for nonpoisonous, high melting point substrate, clad or core materials desirable for melt processing of Y‐Ba‐Cu‐O.

ISSN:0003-6951    

DOI:10.1063/1.103255

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An increase by over three orders of magnitude from 0.58 m&OHgr; to 1.17 &OHgr; was observed at 4.0 K in the 3 GHz microwave surface resistance of ceramic YBa2Cu3O7−&dgr;following exposure to neutrons. The transport resistivity of an unirradiated pellet was linear in temperature down toTcwith a room‐temperature value of 2.13 m&OHgr; cm and a resistivity extrapolated to 4.0 K of 0.53 m&OHgr; cm. Following irradiation, the resistivity rose with decreasing temperature from a room‐temperature value of 1.5 &OHgr; cm to a maximum at around 45 K with little change evident atTc. These results, in conjunction with eddy current, susceptibility, iodometric titration, and thermally stimulated luminescence measurements on irradiated and unirradiated samples, collectively suggest that the effect of neutron irradiation has been to decrease intergranular coupling without the development of an insulating phase.

ISSN:0003-6951    

DOI:10.1063/1.103256

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have measured the pinning force due to twin boundaries by measuring the magnetic torque produced when a field is applied perpendicular to thecaxis and rotated with respect to theabaxes. At 76 K, the torque increases roughly fourfold, when the field is within 2° of the parallel to the twin boundaries. This peak is absent at 27 K. Irradiation with 5×1016cm−23.5 MeV protons increases the overall critical current and eliminates the peaks observed at 76 K.

ISSN:0003-6951    

DOI:10.1063/1.103257

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have studied the correlations between deposition parameters and structural and electrical properties of YBa2Cu3O7−&dgr;thin films growninsituby sequential ion beam sputtering. Epitaxial,c‐axis oriented YBa2Cu3O7−&dgr;films were grown both on (100) SrTiO3and on (100) MgO substrates following the stacking sequence of the ‘‘123’’ compound, with deposited layer thicknesses nominally equal to 1 monolayer. Thec‐axis lattice parameters obtained were larger than the corresponding lattice parameter in bulk samples, even after low‐temperature anneals in O2. The transition temperatures were found to decrease with the enlargement of thec‐axis lattice parameter. A clear correlation between growth temperature and the value of thec‐axis lattice parameter was observed. Thec‐axis lattice parameter and the x‐ray linewidth of Bragg reflections with theGvector along thec‐axis were also found to be correlated. This suggests a relationship between thec‐axis lattice parameter and the structural coherence of the epitaxial films.

ISSN:0003-6951    

DOI:10.1063/1.103258

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High‐voltage waveforms with rise times of 50 ns were produced by electromagnetic shock‐wave generation in a uniform, lumped element delay line constructed with nonlinear, ferroelectric capacitors. A close correlation was found between the experimental voltage waveforms observed at different positions along the delay line and those predicted by a numerical computer code.

ISSN:0003-6951    

DOI:10.1063/1.102907

出版商:AIP    

年代:1990

数据来源: AIP